In the retreading of tires, two methods are commonly used. In a tire mold method after preparation of the tire carcass, the carcass and uncured rubber are placed in a retreading mold. The mold shapes the uncured rubber into the desired tread pattern. The assembly is cured while in mold.
In the second method, to which the present apparatus is directed, a precured tread strip is applied to the prepared carcass together with an intermediate thin layer of uncured rubber. This assembly is then placed into a flexible elastomeric envelope which encases a portion of the carcass and the precured tread stock. Normally, the tire is mounted on a rim prior to enclosing the assembly with the flexible envelope. In addition to the rim, an inner tube is normally positioned within the tire carcass. Finally the entire assembly is positioned within an autoclave to cure the intermediate layer thus joining the precured tread to the tire carcass.
It has been found that the rim and tube acts as a thermal barrier and heat sink during the curing process and substantially lengthens the curing time. It is not unusual to have an eight hour curing cycle for a truck tire retreading operation.